# Improve efficiency: Was it worth it?

**URL:** <https://community.openenergymonitor.org/t/improve-efficiency-was-it-worth-it/13386>\
**Category:** Heatpump\
**Created:** [20 February 2020 19:53 UTC](https://community.openenergymonitor.org/t/improve-efficiency-was-it-worth-it/13386 "2020-02-20T19:53:27Z")\
**Posts on this page:** 1\
**Showing post:** 31

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**Author:** ![Steve](https://community.openenergymonitor.org/letter_avatar_proxy/v4/letter/s/f19dbf/32.png) [@Steve](https://community.openenergymonitor.org/u/Steve)\
**Post date:** [27 February 2020 20:29 UTC](https://community.openenergymonitor.org/t/improve-efficiency-was-it-worth-it/13386/31 "2020-02-27T20:29:31Z")

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The simple integrating controller in my non-modulating Thermia ground/underfloor heatpump works well. The greater the demand, the longer the compressor stays on.

In process control language it’s a cut-down [PID controller](https://en.wikipedia.org/wiki/PID_controller#Integral) (Wikipedia). Here’s a real-life example:

1. Choose a target for the circulating water. Right now the outside temperature is 3 degrees C and the target is 26 degrees.

2. Calculations

- The integral is an accumulator which starts at 0 at switch-on.

- Once a minute, measure the difference between the flow pipe to the underfloor and the set point. (Not the return because that varies less.) This difference is the “error” in process control.

- If the flow temperature is X degrees below the set point, subtract X from the accumulator.

- Or if the flow is X degrees above the set point, add X to the accumulator.

1. Decisions, also once per minute

- If the accumulator is -60 or below, turn on the compressor.
- If the accumulator is between -60 and 0, leave the compressor in its current state (on or off).
- If the accumulator is 0 or greater, turn off the compressor.
- If the error is greater than 10 (i.e. too hot) turn off the compressor.

The thresholds at 0 and -60 provide hysterisis, and are adjustable.  
The relationship between outside temperature and set point is also adjustable - typically a drop of 1 degree in outside temperature should increase the set point by 2 or 3.

Might be some ideas for you heat pump owners there.

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